Re: [tip:x86/urgent] x86: Make 64-bit efi_ioremap use ioremap on MMIO regions

[Huang Ying <ying.huang@intel.com>]

On Tue, 2009-08-04 at 09:51 +0800, Paul Mackerras wrote:
> Huang Ying writes:
> 
> > This patch does not really fix the issue. __cpa_process_fault will warn
> > if target memory area is beyond max_pfn_mapped. EFI runtime RAM area
> > beyond max_pfn_mapped will trigger the warning too.
> 
> I think we already have that situation on that MacBook, and there is
> no warning.  From dmesg:
> 
> [    0.000000] EFI: mem190: type=9, attr=0xf, range=[0x000000007fedf000-0x000000007feef000) (0MB)
> [    0.000000] EFI: mem191: type=7, attr=0xf, range=[0x000000007feef000-0x000000007fef9000) (0MB)
> [    0.000000] EFI: mem192: type=0, attr=0xf, range=[0x000000007fef9000-0x000000007feff000) (0MB)
> [    0.000000] EFI: mem193: type=6, attr=0x800000000000000f, range=[0x000000007feff000-0x000000007ff00000) (0MB)
> ...
> [    0.000000] last_pfn = 0x7fef9 max_arch_pfn = 0x400000000
> ...
> [    0.000000] initial memory mapped : 0 - 20000000
> [    0.000000] init_memory_mapping: 0000000000000000-000000007fef9000
> [    0.000000]  0000000000 - 007fe00000 page 2M
> [    0.000000]  007fe00000 - 007fef9000 page 4k
> [    0.000000] kernel direct mapping tables up to 7fef9000 @ 8000-c000
> ...
> [    0.001920] init_memory_mapping: 000000007feff000-000000007ff00000
> [    0.001926]  007feff000 - 007ff00000 page 4k
> 
> So the initial mapping ends at 0x7fef9000, and I believe that
> max_pfn_mapped is 0x7fef9, and then EFI asks for pfn 0x7feff to be
> mapped.  But I freely admit this is not my area of expertise.  This
> machine has 2GB of RAM, by the way.

If you specify "mem=<xxx>m" to a small value in kernel command line, I
think the kernel warning will appear again. Because some EFI runtime
memory area may be beyond max_pfn_mapped.

> > To fix the issue. I think we can loose the restriction of
> > __cpa_process_fault a little. Add a global variable max_pfn, which is
> > max pfn of all memory type (including RAM, RESERVED, etc, mapped or
> > unmapped), and __cpa_process_fault warns for memory area beyond max_pfn
> > only.
> 
> It seemed cleaner to me to use ioremap() on areas that we are told are
> MMIO.  Why would it be better to use init_memory_mapping for those
> areas?

I prefer init_memory_mapping because it is more compatible with KEXEC
support (not done yet). Because EFI runtime memory area should be mapped
in exactly same position in original and kexeced kernel.

Best Regards,
Huang Ying